The invention relates to a method for detecting locking states in communication and/or control apparatuses which are networked to one another in a distributed manner using a data bus.
The invention also relates to a communication and/or control apparatus having an interface for connection to a data bus and networking to further communication and/or control apparatuses.
In complex technical systems in which communication and/or control apparatuses are networked to one another via a data bus, the readiness to transmit and the functionality of the communication and/or control apparatuses must be regularly monitored. This is indispensable, in particular, for safety-critical applications in motor vehicles, for example airbag control apparatuses etc.
To this end, it is first of all possible to evaluate whether messages are regularly transmitted by the communication and/or control apparatuses.
However, a problem arises when the communication and/or control apparatuses are in a locking state and transmit messages even though the communication and/or control apparatus is blocked and can no longer perform its actual task. A locking state is a state in which two processes which are respectively assigned an operating means are waiting for the respective other process to enable the operating means, for example, and both processes thus block one another. Although they are thus still able to regularly transmit messages, they are blocked from carrying out the actual process.
JP 11163905 A discloses a method for the multiplexed transmission of data via a data bus in a motor vehicle, in which changes in the data are detected and are indicated using an update bit.
JP 11163903 A also discloses a method for the multiplexed transmission of data via a data bus in a motor vehicle, in which the connection of a communication unit of the calling subscriber to the data bus is detected and the data are only then transmitted.
In the conventional methods, locking states are detected by concomitantly transmitting, together with the message to be transmitted, a monitoring signal from the transmitter, for example a message counter. This additional information is not used to transmit function contents or function signals but merely for monitoring purposes in order to be able to detect a possible locking state of the transmitting communication and/or control apparatus in a communication and/or control apparatus that receives the message. This additional information disadvantageously increases the length of the message and disadvantageously increases the data bus utilization level.
Therefore, it is an object of the invention to provide an improved method for detecting locking states in communication and/or control apparatuses which are networked to one another in a distributed manner using a data bus, the utilization level of the data bus being intended to be reduced by reducing the length of the message.
It is also an object of the invention to provide a correspondingly improved communication and/or control apparatus.